Noncollinear phase of the antiferromagnetic sawtooth chain
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arXiv
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| Format: | Preprint |
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2024
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| _version_ | 1866916582538608640 |
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| author | Rausch, R. Karrasch, C. |
| author_facet | Rausch, R. Karrasch, C. |
| contents | The antiferromagnetic sawtooth chain is a prototypical example of a frustrated spin system with vertex-sharing triangles, giving rise to complex quantum states. Depending on the interaction parameters, this system has three phases, of which the gapless non-collinear phase (for strongly coupled basal spins and loosely attached apical spins) has received little theoretical attention so far. In this work, we comprehensively investigate the properties of the non-collinear phase using large-scale tensor network computations which exploit the full SU(2) symmetry of the underlying Heisenberg model. We study the ground state both for finite systems using the density-matrix renormalization group (DMRG) as well as for infinite chains via the variational uniform matrix-product state (VUMPS) formalism. Finite temperatures and correlation functions are tackled via imaginary- or real time evolutions, which we implement using the time-dependent variational principle (TDVP). We find that the non-collinear phase is characterized by a low-momentum peak and a diffuse tail for the apex-apex correlations. Deep into the phase, the pattern sharpens into a peak indicating a 90-degree spiral. The apical spins are soft and highly susceptible to external perturbations; they give rise to a large number of gapless magnetic states that are polarized by weak fields and cause a long low-temperature tail in the specific heat. The dynamic spin-structure factor exhibits additive contributions from a two-spinon continuum (excitations of the basal chain) and a gapless peak at $k=π/2$ (excitations of the apical spins). Small temperatures excite the gapless states and smear the spectral weight of the $k=π/2$ peak out into a homogeneous flat-band structure. Our results are relevant, e.g., for the material atacamite Cu$_2$Cl(OH)$_3$ in high magnetic fields. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2402_05759 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Noncollinear phase of the antiferromagnetic sawtooth chain Rausch, R. Karrasch, C. Strongly Correlated Electrons The antiferromagnetic sawtooth chain is a prototypical example of a frustrated spin system with vertex-sharing triangles, giving rise to complex quantum states. Depending on the interaction parameters, this system has three phases, of which the gapless non-collinear phase (for strongly coupled basal spins and loosely attached apical spins) has received little theoretical attention so far. In this work, we comprehensively investigate the properties of the non-collinear phase using large-scale tensor network computations which exploit the full SU(2) symmetry of the underlying Heisenberg model. We study the ground state both for finite systems using the density-matrix renormalization group (DMRG) as well as for infinite chains via the variational uniform matrix-product state (VUMPS) formalism. Finite temperatures and correlation functions are tackled via imaginary- or real time evolutions, which we implement using the time-dependent variational principle (TDVP). We find that the non-collinear phase is characterized by a low-momentum peak and a diffuse tail for the apex-apex correlations. Deep into the phase, the pattern sharpens into a peak indicating a 90-degree spiral. The apical spins are soft and highly susceptible to external perturbations; they give rise to a large number of gapless magnetic states that are polarized by weak fields and cause a long low-temperature tail in the specific heat. The dynamic spin-structure factor exhibits additive contributions from a two-spinon continuum (excitations of the basal chain) and a gapless peak at $k=π/2$ (excitations of the apical spins). Small temperatures excite the gapless states and smear the spectral weight of the $k=π/2$ peak out into a homogeneous flat-band structure. Our results are relevant, e.g., for the material atacamite Cu$_2$Cl(OH)$_3$ in high magnetic fields. |
| title | Noncollinear phase of the antiferromagnetic sawtooth chain |
| topic | Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2402.05759 |